The escalating demand for sustainable environmental remediation techniques has spurred significant research into the application of biowastes as biochar and biosorbents for heavy metal removal and precious metal recovery. The present review offers a detailed overview of the different sources of precious metals and heavy metals, evaluates the potential of biowastes as sustainable resources, and explains various strategies for producing and modifying innovative biosorbents and biochar to tackle key environmental challenges. Considerable attention is dedicated to the innovative utilization of biochar-derived composites as a promising approach to enhance metal removal efficiency (Zn, Cu, and Pb up to 99.96 %, 99.99 %, and 99.75 %, respectively, using Na₂CO₃, Ca (OH)₂, and Na₂S). Functionalized biochars are combined with other materials, such as activated carbon or metal oxides to exhibit synergistic effects for improving their adsorption capacity and selectivity for precious metals. The highest biosorption capacities for various metals were 558.9, 103.5, and 443.0 mg/g for sugarcane bagasse, cellulose fiber, Sargassum filipendula, and coconut husk. Low pyrolysis (60–80 %) and hydrothermal carbonization (30–70 %) produce biochar as byproducts for metal adsorption, but they also add value by simultaneously generating syngas and bio-oil. Additionally, the review discusses the economic and environmental benefits of utilizing biowastes, emphasizing their role in promoting the circular economy. Case studies demonstrating successful implementation in various industrial and environmental contexts are presented. Future perspectives are outlined identifying research gaps and potential pathways for further advancement and application of biomass-derived biosorbents and biochar. This comprehensive analysis underscores the transformative potential of biowaste-based solutions for maximum removal of heavy metals and precious metal recovery, thereby providing more sustainable and efficient environmental management practices.